Given a DPDT relay rated at .5A @ 120VAC,
Using 24VAC instead of 120V,
Does it compute that the relay will handle 2.5A @ 24VAC ?

(i.e., 120/24 * .5A = 2.5A)

Or is that bad math?

Here's the full specs, if it matters:
http://www.altronics.com.au/download/ndb/brochures/s/S4150.PDF

Meisei m4-24h
1A 24V DC / .5A 120V AC
Max ratings
Power 60W DC / 120VA AC
Switching Current 2A DC/AC

 

Hello,

It already tells you in your datasheet.

Contacts
Arrangement.......................................................................... 2 Form C
Type ......................................................................Bifurcated Crossbar
Material
Movable Contact ................................Gold clad Silver-Palladium Alloy
Stationary Contact..............................Gold clad Silver-Palladium Alloy
Ratings (Resistive Load) ..........................1A 24V DC / 0.5A 120V AC
Max. Ratings (Resistive Load)
Max. Switching Power..........................................60W DC / 125VA AC
Max. Switching Voltage ........................................220V DC / 250V AC
Max. Switching Current ......................................................2A DC / AC
Min. Switching Load ..................0.01mA 10mV DC (Reference Value)
Expected Life (Min. Operations)
Mechanical............................................................................100 million
Electrical (Resistive Load) ............................0.5 million at 1A 24V DC
0.2 million at 0.5A 120V AC
Contact Resistance ..............................................50mΩ Max. at initial

Greetings,
Bertus

 

The answer was given by bertus but i want to add that the current rating of a relay is not calculated like the way you did it. The voltage rating for a relay is not given to calculate the power rating but not to apply a voltage greater than this voltage because you will create sparks on the contacts. Of course the voltage plays a little role on how much current the contacts can carry but because they have very low resistance the power dissipated by them is almost the same even with low and high voltages.